Pro Lots of depth
EUIV is a simulation of global politics and war. There is a relatively limited set of choices you can make under normal circumstances: hiring advisors to improve your capabilities, hiring troops, about two dozen diplomatic actions in peace, and a number of different peace deal options when terminating a war. However, these interact to produce a large number of interesting decisions that affect your outcomes.
If you want to annex a neighbor, do you declare a holy war on them, or do you fabricate claims on their territory and demand that they "return" this land to you? Do you ally a much larger nation that might try to force you to be their vassal? Conversely, do you try to improve relations with a much smaller neighbor in order to become their suzerain overlord, or do you attempt to conquer them directly and risk pulling their larger allies into a war?
On top of that, there are hundreds of events that can occur once certain preconditions are met. Some of them are specific to which country you're playing as. Some require you to hire the right set of advisors.
And if you don't keep your country's internal affairs in order, you may find yourself on the wrong end of a peasant's war or facing other national disasters.
Pro Pausable/adjustable speed RTS
Play straight through on real-time, or pause for as much micro-management as is needed. No rapid attacks and the key here, it is pausable even though it can be a real time system. Basically time can be slowed, sped up and paused with most gameplay taking place somewhere in between.
Con Steep learning curve
When you start out, it can be overwhelming. You have a country and three thousand infantrymen -- what can you do? You decide to attack your neighbor -- and they cut you down like reeds. You start over as a bigger country and attack a smaller neighbor -- and suddenly you're in a war against several large countries at once. You start again and this time you find a weak neighbor with no allies. You crush them and bring them under your control -- and suddenly you find revolutions popping up everywhere.
Even after you've learned the basics, you'll still find yourself wondering: if I declare a holy war, will it cost me diplomatic power to annex territory or not? And it's often hard -- certainly in ironman mode -- to undo decisions, so small mistakes and misclicks can end up costing you a lot.
The game does give you guidance in the form of alert bubbles in the upper left of the screen, informing you of the things it thinks are most relevant, and paying attention to those can at least show you what you might want to think about. In the later patches, the user interface has been improving to help reduce surprises -- and the game mechanics as well. For instance, rebel uprising progress can be tracked easily -- you won't be surprised by a sudden uprising of Najdi nationalists, and when you're in for a long-term peasant revolt, the game will tell you why it's happening, how to prevent it, and how to get out of it once it happens.
But simply finding all these parts of the user interface takes time playing. Determining what's important takes experience. You can pause the game at any time and find all the data you can handle, but if you're not just extracting the important parts, the deluge won't help.
Your best bet is to find videos of people playing the game with a bit more skill than you. Streaming is best -- you can ask questions, and most streamers will answer.